package practice4;

import java.util.Scanner;

public class P2311 {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        if(n<20){
            long[] arr=new long[n+2];
            arr[1]=1;
            arr[2]=1;
            for(int i=3;i<=n+1;i++){
                arr[i]=arr[i-1]+arr[i-2];
            }
            System.out.printf("%.8f",arr[n]*(1.0)/arr[n+1]);
        }else{
            System.out.println(0.61803399);
        }
    }
}
